Along the craggy peaks of the Andes from Chile into Argentinia, and down into Patagonia grows a strange alpine plant discovered by Charles Darwin himself. It is known scientifically as Calceolaria uniflora but goes by the common name of 'Darwin's Slipper.' And what a neat little species it is. It stands as an ornate example of a rather unique pollination syndrome, one that that is quite apt considering who discovered it. As with any strange flower, once you begin to ponder the significance of its morphology, you inevitably come to the same question; what on Earth pollinates it?

As a whole the genus Calceolaria is bee pollinated. Relying on what are known as "oil bees," most of the flowers in this genus produce hairs that secret oils that the female bees relish. Calceolaria uniflora is rather different from the rest. Instead of producing flowers with a tube or a pouch, this species creates an almost alien-looking red and orange bloom with a bright white appendage on its lower lip. What is going on there? The answer to this strange riddle has a clue in where this species grows.

At high altitudes, oil-collecting bees are rather scarce. It is simply too cold and harsh for many insects to survive at such elevations. Instead, what are present are birds, specifically a species of seedsnipe. These little birds exist on a plant-based diet and spend a lot of their time holding territories and grazing on seeds and fruits of a handful of alpine plants. Researchers noticed that patches of Calceolaria uniflora growing around these birds seemed to have high levels of floral damage, specifically on the lower lip where the white appendage is located. In fact, the white appendage was often completely removed.

As it turns out, the seedsnipes regularly visit patches of these flowers and proceed to peck off and eat the white appendage. As the birds peck off these appendages, the sexual parts of the flower bash against the birds head. As it does, pollen is dusted onto the bird as well as onto the female parts of the flower. Thus pollination is achieved. But what's in it for the birds? As it turns out, when tested in the lab, researchers found these appendages to be high in sugars. The birds are in it for an easy, sugary meal.

When we think of birds as pollinators, we often think of hummingbirds or honeyeaters. The relationship between Calceolaria uniflora and the seedsnipe is rather outlandish in comparison but it certainly works for both species. The lack of insect pollinators has driven Calceolaria uniflora towards an alternative pollinator and quite a unique one at that!